The invention relates to a moisture curable, hot melt composition, to a method for the manufacture of the moisture curable, hot melt composition, to a cured adhesive composition based on the moisture curable, hot melt composition and to articles bonded with the moisture curable, hot melt composition.
Isocyanate-terminated polyurethane prepolymers (sometimes referred to hereinafter as xe2x80x9cpolyurethane prepolymersxe2x80x9d or xe2x80x9cprepolymersxe2x80x9d) are desirable in a variety of applications. For example, they can be used in reactive hot melt urethane adhesive, coating and/or sealant systems. Hot melt urethane systems are solid at room temperature, melt to a viscous liquid when heated to moderate temperatures (e.g., 55xc2x0 C.-121xc2x0 C.), and are applied in a molten state to an appropriate substrate. On the substrate, the adhesive cools to a solid state to provide an initial bond strength (sometimes referred to as xe2x80x9cgreen strengthxe2x80x9d), and eventually the adhesive will achieve its ultimate bond strength in a curing reaction with ambient moisture. In the presence of an appropriate catalyst, typically a tin-based catalyst, urethane hot melts have rapid rates of cure and provide excellent final properties when cured. Other advantages associated with hot melt adhesives include rapid green strength, bonding without fixturing, and adhesion to a wide variety of substrates While widely used, hot melt urethanes have not been problem-free. These adhesive systems may contain a level of free monomeric isocyanate that can raise concerns regarding possible toxicity. Toxicity issues may become especially important in the application of hot melt adhesives to substrates using spraying and other dispensing methods for applying a hot melt adhesive to a substrate at high temperatures ( greater than 275xc2x0 F.). Because of the foregoing concerns, the use of urethane hot melts has been banned from some industrial sites. In addition to toxicity issues, urethane hot melt adhesives emit carbon dioxide during the curing process. The generation of carbon dioxide in amorphous adhesives can cause undesired bubble formation in the body of the adhesive during the curing process. Problems have also been noted in the otherwise accepted use of tin based catalysts for catalyzing the curing reaction of polyester urethane hot melts. For example, the presence of tin in a urethane hot melt that is based on one or more polyester monomers can adversely affect the hydrolytic stability of the polyester and the thermal stability of the prepolymer.
In one approach to addressing the foregoing toxicity issue, some urethane hot melt adhesives have been end capped with an organo-functional silane to reduce the potential for significant isocyanate toxicity. Such adhesives still require the use of tin-based catalysts to generate acceptable cure rates through the organo-silane groups.
It is desirable to provide a polyester based hot melt adhesive that can be manufactured without the need for a tin-based catalyst but which also has an acceptable and relatively rapid rate of cure.
In a first aspect, the invention provides a moisture curable, hot melt composition comprised of the product of reacted components, the components comprising:
(a) a semi-crystalline polyol;
(b) an essentially amorphous polyol selected from the group consisting of polyols having branched primary hydroxyl groups, polyols having secondary hydroxyl groups, and combinations of the foregoing;
(c) a secondary aminosilane endcapper comprising secondary amnino functionality;
(d) an isocyanate; and
(e) substantially no tin.
In another aspect, the invention provides a method for the manufacture of a moisture curable, hot melt adhesive and/or sealant composition, the method comprising:
(a) preparing a prepolymer by:
(i) mixing a semi-crystalline polyol, an essentially amorphous polyol, an isocyanate and, optionally, a non-tin catalyst, the essentially amorphous polyol selected from the group consisting of polyols having branched primary hydroxyl groups, polyols having secondary hydroxyl groups and combinations thereof;
(ii) reacting the mixture to provide the prepolymer;
(b) reacting the prepolymer with a secondary aminoalkoxysilane endcapper comprising secondary amino functionality to provide the moisture curable, hot melt adhesive and/or sealant composition; and
the steps (a) and (b) are accomplished in the absence of tin catalyst.
In the foregoing aspects of the invention, the semi-crystalline polyol may be a polyester-based polyol selected from a variety of materials including polyhexamethylene sebacate, polyhexamethylene adipate, polybutylene adipate, polyhexamethylene dodecanedioate, poly-epsilon-caprolactone, and combinations thereof. The semi-crystalline polyol comprises the reaction product of a diol and a polyacid (e.g., a dicarboxylic acid). The essentially amorphous polyol may comprise a copolymer of ethylene oxide and propylene oxide, partially end capped with ethylene oxide and having a hydroxyl number between about 10 and about 100. The amorphous polyol can have a crystallinity index less than or equal to about 0.25. In some embodiments, the essentially amorphous polyol comprises a mixture of primary hydroxyl-containing and secondary hydroxyl-containing materials. The isocyanate may comprise a material selected from the group consisting of aliphatic isocyanates, aromatic isocyanates, derivatives of aliphatic isocyanates, derivatives of aromatic isocyanates and combinations of the foregoing. The foregoing adhesive may be provided in a variety of configurations such as a film, for example.
The secondary arninosilane endcapper may comprise any of a variety of silane including N-alkyl-aminoalkyl-alkoxysilane selected from the group consisting of N-methyl-3-amino-2-methylpropyltrimethoxysilane; N-ethyl-3-anino-2-methylpropyltrimethoxysilane; N-ethyl-3-amino-2-methylpropyldiethoxymethylsilane; N-ethyl-3-amino-2-methylpropyltriethoxysilane; N-ethyl-3-amino-2-methylpropyldimethoxymethylsilane; N-butyl-3-amino-2-methylpropyltrimethoxysilane; N-ethyl4-amino-3,3-dimethylbutyldimethoxymethylsilane; N-ethyl-4-amino-3,3-dimethylbutyltrimethoxysilane and combinations of the foregoing. In general, the secondary aminosilane endcapper comprises a material having the formula:
xe2x80x83R0xe2x80x94NR1xe2x80x94R2xe2x80x94Si(OR3)m(R4)n
where R0 is aliphatic,
R1 is hydrogen,
R2 is a straight, branched, or cyclic aliphatic chain,
R3 and R4 are C1-C6 alkyl,
m=1-3, and
n=0-2.
In one preferred embodiment, the (a) the semi-crystalline polyol is polyhexamethylene adipate; (b) the essentially amorphous polyol is a polyoxypropylene glycol comprising secondary hydroxyl groups; (c) the secondary aminosilane endcapper is N-ethyl-3-amino-propyltrimethoxysilane; and (d) the isocyanate is 4,4xe2x80x2-diphenylmethane diisocyanate.
In another aspect of the invention, a cured adhesive and/or sealant composition is provided, derived from the curable, hot melt adhesive and/or sealant composition described above.
In still another aspect of the invention, a curable, hot melt adhesive is provided by the foregoing method of manufacture, and upon curing, provides a cured adhesive derived therefrom.
In still another embodiment of the invention, a bonded article is provided, comprising:
a first substrate;
a second substrate; and
the foregoing cured adhesive composition (derived from the foregoing moisture curable, hot melt composition) between the first substrate and the second substrate and affixing the first and second substrates to one another.
In still another aspect, the invention provides a tape comprising a backing and having the aforementioned moisture curable, hot melt composition associated with at least one major surface of the backing.
Other features of the invention will be more fully appreciated by those skilled in the art upon consideration of the remainder of the disclosure including the Detailed Description of the Preferred Embodiment, including the Examples and the appended claims.
The present invention relates to hot melt adhesives and coatings. In general, adhesives of the invention comprise a product of reacted components. In broad terms, the components comprise (a) a semi-crystalline polyol; (b) an amorphous polyol comprising hydroxyl groups, typically secondary hydroxyl groups; (c) an isocyanate; (d) an aminoalkoxysilane endcapper comprising secondary amino functionality; and (e) substantially no tin. The adhesive generally requires the preparation of a isocyanate-terminated polyurethane prepolymer using the components (a), (b) and (c). The isocyanate moieties of the prepolymer are reacted with an aminoalkoxysilane endcapper to provide an aminoalkoxysilanexe2x80x94capped hot melt adhesive with reduced isocyanate toxicity issues, is thermally stable with an extended open time, is resistant to aging and yellowing and, when applied to a surface, cures rapidly to provide strong adhesive bonding.
The semi-crystalline polyol (herein xe2x80x9cComponent Axe2x80x9d) of the moisture curable, hot melt adhesive and/or sealant composition is most typically a polyester. Useful polyester monomers include essentially linear, saturated aliphatic material that is at least semicrystalline. By xe2x80x9csemicrystallinexe2x80x9d it is meant that Component A exhibits both a crystalline melting point (Tm) and a glass transition temperature (Tg), and has a crystallinity index of greater than 0.25. In some embodiments, the crystallinity index is greater than 0.30.
The crystallinity index of a polymer, as used herein, should be understood as being defined in a manner consistent with the understanding of those skilled in the art. As such, the crystallinity index may be defined as the fraction of crystalline material present in a sample of the polymer. A crystallinity index of 1.0 is taken as representing 100% crystallinity and a value of zero corresponding to a completely amorphous material. Crystalline indices have been determined using x-ray diffraction data for the adhesives described herein using a Philips vertical diffractometer (available from Philips Analytical, Natick, Mass.), a copper Kxcex1 (xe2x80x9cKalphaxe2x80x9d) radiation source, and a proportional detector registry of the scattered radiation. In determining crystallinity indices herein, a diffractometer was fitted with variable entrance slits, a diffracted beam graphite monochromator, and fixed exit slits. An x-ray generator was operated at 45 kilovolts (kV) and 30 milliAmperes (mA) to power a copper target x-ray tube. Data were collected in a reflection geometry from 5 to 55 degrees (corresponding to an angle of xe2x80x9c2 thetaxe2x80x9d) using a 0.04 degree step size and 8 second dwell time. Samples of the polyols were prepared for x-ray analysis as thin smears on zero background specimen holders made of single crystal quartz. The program ORIGINS(trademark) (Version 4.1, available from Microcal Software Incorporated, Northhampton, Mass.) was used to perform profile fitting of the diffraction pattern and to measure diffraction peak area values. A Gaussian peak shape model and linear background model were employed to describe the individual crystalline peak and amorphous peak contributions. Crystallinity indices were calculated as the ratio of crystalline peak area to total (crystalline+amorphous) scattered peak area within a 6 to 36 degree (corresponding to an angle of xe2x80x9c2 thetaxe2x80x9d) scattering angle range.
Component A may have a melting temperature (Tm) between about 5xc2x0 C. and 120xc2x0 C. and generally between about 40xc2x0 C. and 105xc2x0 C. Additionally, Component A typically will have a glass transition temperature (Tg) below about 0xc2x0 C. If Component A is provided in the form of a polyester polyol, it may comprise the reaction product of (1) a polyol such as, for example, a diol, and (2) a polyacid, for example, a dicarboxylic acid. Alternatively, Component A may comprise the oligomer of a ring opened lactone such as, for example, polycaprolactone.
Component A will typically hake a number average molecular weight (Mn) of at least about 2000, generally at least between about 2200 and about 10,000, and in specific embodiments between about 2500 and about 8500. At an Mn below about 2000, the resultant prepolymer is soft and may lack cohesive strength in the uncured state. At an Mn above about 10,000, the resultant prepolymer can be viscous at the application temperature of the composition. If so, it may be more difficult to deposit acceptably thin lines of adhesive on a substrate. The application temperature may be, for example, a temperature between about 200xc2x0 F. (93xc2x0 C.) and 300xc2x0 F. (149xc2x0 C.).
Suitable diols useful in preparing the hydroxy-functional material Component A include, for example, those having from 2 to 12 methylene groups such as ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, and 1,10-decanediol. Cycloaliphatic diols such as, for example, 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol may also be employed.
Suitable dicarboxylic acids useful in preparing the hydroxy-functional material of Component A include, for example, those having from about 2 to 10 methylene groups such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, and 1,12-dodecanedioic acid. Included within the scope of useful acids are acid derivatives such as acid anhydrides, acid halides, and alkyl esters such as, for example, the methyl and ethyl esters.
Certain examples of a suitable Component A of the invention include, for exarnple, polyhexamethylene sebacate, polyhexamethylene adipate, polybutylene adipate, polyhexamethylene dodecanedioate, poly-epsilon-caprolactone, and combinations thereof. In some embodiments, the essentially semicrystalline polyester polyol is polyhexamethylene sebacate or polyhexamethylene adipate. In specific embodiments, the essentially semicrystalline polyester polyol is polyhexamethylene adipate which is the reaction product of 1,6-hexanediol and adipic acid.
Examples of commercially available essentially semicrystalline polyester polyols useful in the invention include, for example, those available under the trade designations RUCOFLEX S-1074P-30 and RUCOFLEX S-105P-30, both available from Ruco Polymer Corporation, Hicksville, N.Y.
Another component for the formation of the polyurethane prepolymer is an essentially amorphous polyol (herein xe2x80x9cComponent Bxe2x80x9d). The amorphous polyol may comprise primary hydroxyl groups on a branched aliphatic chain, secondary hydroxyl groups and/or combinations of the foregoing. Most typically, the amorphous polyol comprises secondary hydroxyl groups. An xe2x80x9cessentially amorphousxe2x80x9d material should be understood to include all amorphous materials and all materials that exhibit a crystallinity index less than or equal to about 0.25, and in some instances exhibit a crystallinity index of no greater than 0.20. Component B may exhibit a weak Tm or it may have no measurable Tm.
Component B may comprise any of a variety a known amorphous polyol materials, such as those commercially available under the trade designation ACCLAIM 2220, a copolymer diol based on propylene oxide and ethylene oxide having a molecular weight of about 2250 and a hydroxyl number between 48.5 and 51.5, commercially available from Bayer Corporation, Pittsburgh, Penn.; those available under the trade designation PPG-1000, also commercially available from Bayer Corporation. Additionally, 2,3-butanediol; 1,2-butanediol; 1,2-propanediol; 2-methyl-1,3-propanediol (MP Diol) as well as combinations of two or more of the foregoing materials and polyester diols derived from the foregoing alkyldiols may also be employed. The amorphous polyol of Component B may comprise a polyoxypropylene glycol partially endcapped with ethylene oxide as well as copolymers of propylene oxide and ethylene oxide partially endcapped with ethylene oxide, such materials having a hydroxy number between about 10 and about 100, and more typically between about 20 and about 60. The foregoing ethylene oxide capped materials contain the desired secondary hydroxyl groups while also exhibiting greater reactivity due to the presence of primary hydroxyl groups. Component B may also comprise mixtures of primary hydroxyl-containing and secondary hydroxyl-containing materials, or alternatively a material that possesses both primary and secondary hydroxyl groups thereon.
Another component used to prepare the isocyanate-terninated prepolymer is an isocyanate material (Component C) which may also be a polyisocyanate. Polyisocyanates used in the formation of the urethane prepolymers may be aliphatic or aromatic. Suitable aromatic polyisocyanates may include aromatic diisocyanates such as diphenylmethane-2,4xe2x80x2-diisocyanate and/or diphenylmethane 4,4xe2x80x2-diisocyanate (MDI); tolylene-2,4-diisocyanate and -2,6-diisocyanate (TDI) and mixtures thereof. Other examples include: naphthylene-1,5-diisocyanate; triphenylmethane-4,4xe2x80x2,4xe2x80x3-triisocyanate; phenylene-1,3-diisocyanate and -1,4-diisocyanate; dimethyl-3,3xe2x80x2-biphenylene-4,4xe2x80x2-diisocyanate; diphenylisopropylidine-4,4xe2x80x2-diisocyanate; biphenylene diisocyanate; xylylene-1,3-diisocyanate and xylylene-1,4-diisocyanate, and mixtures thereof.
Other useful polyisocyanates are known to those skilled in the art and may include one or more of the polyisocyanates found in the Encyclopedia of Chemical Technology, Kirk-Othlmer, 2nd Ed., vol. 12, pp. 46-47, Interscience Pub., N.Y. (1967), the disclosure of which is incorporated herein by reference thereto. Isocyanate-functional derivative(s) of MDI and TDI may be used, such as liquid mixtures of the isocyanate-fiuctional derivative with melting point modifiers (e.g., mixtures of MDI with polycarbodiimide adducts such as that known under the trade designation ISONATE 143L, commercially available from Dow Chemical Company of Midland Mich.). Small amounts of polymeric diphenylmethane diisocyanates may be included, generally 10% or less by weight of the total isocyanate components including those known as PAPI and the series PAPI 20 commercially available from Dow Chemical Company, the MONDUR MR and MRS series of isocyanates commercially available from Bayer Chemical Corporation, and RUBINATE M isocyanates, commercially available from Huntsman Chemical Company of Houston, Tex. Blocked isocyanate compounds formed by reacting aromatic isocyanates or the above-described isocyanate-functional derivatives with blocking agents such as ketoximes and the like may also be useful as Component C within the invention.
The foregoing Components A, B, and C are used in the formulation of a polyurethane prepolymer. An alkoxysilane endcapper (Component D) is used to react with isocyanate end groups of the polyurethane prepolymer to provide a hot melt adhesive that avoids the aforementioned problems associated with isocyanatexe2x80x94terminated urethanes. The silane endcapper used in the present invention may include any of a variety of (N-alkyl-aminoalkyl)-alkoxysilane materials such as the following secondary aminosilanes:
N-methyl-3-amino-2-methylpropyltrimethoxysilane,
N-ethyl-3-amino-2-methylpropyltrimethoxysilane,
N-ethyl-3-amino-2-methyl propyldiethoxymethylsilane,
N-ethyl-3-amino-2-methylpropyltriethoxysilane,
N-ethyl-3-amino-2-methylpropyldimethoxymethylsilane,
N-butyl-3-amino-2-methylpropyltrimethoxysilane,
N-ethyl-4-amino-3,3-dimethylbutyldimethoxymethylsilane,
N-ethyl-4-amino-3,3-dimethylbutyltrimethoxysilane.
The foregoing alkoxysilane materials and others useful as an endcapper herein may be generally represented by the structure:
R0xe2x80x94NR1xe2x80x94R2xe2x80x94Si(OR3)m(R4)n
Where R0 is aliphatic, R1 is hydrogen, R2 is a straight, branched, or cyclic aliphatic chain, R3 and R4 are C1-C6 alkyl, m=1-3, and n=0-2.
The polyurethane prepolymers used herein have an organic backbone with unreacted isocyanate groups that are easily silylated by endcapping with an aminosilane. In particular, aminoalkoxysilanes having a secondary amino functionality react readily with the isocyanate groups of the urethane prepolymers to provide inventive adhesives which possess stable urea linkages formed by reaction between the isocyanate and secondary amine functionalities, and which have the desired properties described herein. In the preparation of the hot melt adhesives of the invention, a urethane prepolymer is first prepared. One or more of the Component A hydroxyl-functional materials are selected along with one or more of the hydroxyl functional materials of as Component B. The hydroxyl function materials are first mixed in a suitable vessel, heated and melted. Once melted, the mixture is stirred to ensure thorough blending and is then further heated under vacuum to dry the blend. Next, the container with the dried blend is again heated under mild or xe2x80x9clowxe2x80x9d heat and stirred while under a nitrogen blanket and isocyanate (Component C) is added in flaked form and mixed into the blend. Most typically 4,4xe2x80x2-diphenylmethane diisocyanate (MDI) is used. A non-tin catalyst may be added with stirring to promote the reaction between MDI and hydroxyl-containing components. One such catalyst is 2,2xe2x80x2-dimorpholinodiethylether (DMDEE), commercially available from Huntsman Chemical Corporation, Houston, Tex. The amount of DMDEE catalyst added to the mixture is low, typically about 0.2% by weight. The exact amount of the catalyst used may vary depending on the combined amounts of Components A, B, C and DMDEE used or employed, and will be known by those skilled in the art.
The foregoing components are stirred to ensure adequate mixing and then are placed in a vacuum oven at 250xc2x0 F. (121xc2x0 C.) for between about 2 and about 3 minutes. For those compositions containing a secondary (2xc2x0) hydroxyl group, the blended mixture is stirred continuously while kept in the vacuum oven for 2 hours to ensure complete reaction of these groups. Next, the resulting isocyanate terminated prepolymer is heated and stirred under a nitrogen blanket.
The silane Component D is added to the foregoing isocyanate terminated prepolymer with stirring and in an amount to provide about 1.2 equivalents of amino hydrogen (from the silane component) per 1.0 equivalent of remaining, unreacted isocyanate functionality. The resulting silane-capped composition is then put into a vacuum oven and is kept there until it stops frothing, typically between 20 and 30 minutes. The resulting silane-capped composition is pourable at elevated temperature and may be placed into an adhesive cartridge (e.g., 0.1 gallon (0.38 liter) aluminum cartridge) which is typically sealed for subsequent use.
Other aspects relating to the manufacture of the adhesives of the invention may be appreciated upon consideration of the Examples set forth below.
It will also be appreciated that other ingredients or adjuvants may be employed with the blends of the invention to impart to or modify particular characteristics of the composition. These ingredients are included in the overall blends or mixtures of the invention rather than being incorporated into the constituent components thereof. The adjuvants should be added only at a level that does not materially interfere with the adhesion of the composition. The adjuvants may comprise up to 50 weight percent of the uncured composition either individually or in combination. For example, chain-extending agents (e.g., short chain polyols such as ethylene glycol or butanediol); fillers (e.g., carbon black; glass, ceramic, metal or plastic bubbles; metal oxides such as zinc oxide; and minerals such as talc, clays, silica, silicates, and the like), thermoplastic resins; plasticizers; antioxidants; pigments; U.V. absorbers; adhesion promoters and the like may be included to modify set time, open time, green strength build-up, tack, flexibility, adhesion, etc.
Typical fillers suitable for formulation of the sealants include reinforcing fillers such as fumed silica, precipitated silica, calcium carbonates, carbon black, glass fibers, aluminasilicate, clay, zeolites and similar material. These fillers can be used either alone or in combination with each other. The fillers generally comprise up to 300 parts per 100 parts of the silylated polymer with 80 to 150 parts being a more preferred loading level.
Plasticizers customarily employed in sealants can also be used in the compositions of the invention to modify the properties of the adhesive and to facilitate use of higher filler levels. Exemplary plasticizers include phthalates, dipropylene and diethylene glycol dibenzoates and mixtures thereof, epoxidized soybean oil and the like. Useful sources of dioctyl and diisodecyl phthalate include those available under the tradenames JAYFLEX DOP and JAYFLEX DIDP from ExxonMobil Corporation, Houston, Tex. The dibenzoates are available commercially under the trade designation BENZOFLEX 9-88, BENZOFLEX 50 and BENZOFLEX 400 from Velsicol Chemical Corporation of Rosemont, Ill. The plasticizer typically comprises up to 100 parts per hundred parts of the silylated polymer with 40 to 80 parts per hundred being preferred.
The adhesive formulation can include various thixotropic or anti-sagging agents. This class of additives are typified by various castor waxes, fumed silica, treated clays and polyamides. These additives typically comprise 1 to 10 parts per hundred parts of silylated urethane component with 1 to 6 parts being preferred. Useful thixotropes include those available as: AEROSIL from Degussa Corp. of Piscataway, N.J. CAB-O-SIL from Cabot Corp. of Tuscola, Ill., CASTORWAX from CasChem, Inc. of Bayonne, N.J., THIXATROL and THIXCIN from Elementis Specialties, Inc. of Heightstown, N.J., and DISPARLON from King Industries of Norwalk, Conn.
UV stabilizers and/or antioxidants can be incorporated into the sealant formulations of this invention in an amount from 0 to 5 parts per hundred parts of silylated urethane polymer with 0.5 to 2 parts being preferred. These materials are available from companies such as Great Lakes Chemical Corp., Indianapolis, Ind. and Ciba Specialty Chemicals Corporation of Tarrytown, N.Y. under the tradenames: ANOX 20 and UVASIL 299 HM/LM (Great Lakes Chemical Corp., Indianapolis, Ind.), and IRGANOX 1010, IRGANOX 1076, TINUVIN 770, TINUVIN 327, TINUVIN 213 and TINUVIN 622 LD (Ciba Specialty Chemicals), respectively.
In addition, the compositions of the invention may include an effective amount of a catalyst or reaction accelerator such as tertiary amines, co-curatives and the like. An effective amount of a catalyst is, for example, from about 0.005 to 2 percent by weight of the total prepolymer weight. In specific embodiments, the catalyst is present at a level of about 0.01 to about 0.5 percent, based on the total weight of the prepolymers employed.
The hot melt adhesives of the invention may be used for bonding surfaces to one another. Wood, metal, glass surfaces as well as certain plastic surfaces (e.g., polyvinylchloride, acrylonitrile/butadiene/styrene terpolymer, polycarbonate) as well as fiber reinforced plastics may be bonded to one another with the described hot melt adhesives. A quantity of the hot melt composition may be applied to a first substrate or surface using a sealed cartridge, typically preheated to about 250xc2x0 F. (121xc2x0 C.) for between 30 and 60 minutes prior to extruding it onto the surface to be bonded. After the adhesive was applied, small diameter (e.g., 0.003-0.005 inch (0.08-0.13 mm)) glass beads or the like may be sparingly applied uniformly on the molten adhesive to control bondline thickness. A bond may be formed by mating the first substrate with another substrate to provide a 0.5 inch by 1.0 inch (1.25 by 2.5 cm) overlap bond area. The substrates may be bonded to one another using pressure such as, for example, firm hand pressure to compress the adhesive to a desired thickness and squeeze excess adhesive from the bond area The assembly should set for several minutes, typically from 5 to 10 minutes. Excess flash (if present) is preferably trimmed from the bottom side of the bonded assembly. At this point, a bond will normally have formed and an initial overlap shear strength may be measured. The bonded substrates should be allowed to cure under ambient conditions for a period of time to achieve an optimum bond strength.